This invention relates to integrated circuit microcontrollers, and, more particularly, to an integrated circuit microcontroller having a configurable operational amplifier as a peripheral.
Integrated circuit microcontrollers are becoming far more sophisticated while continuing to drop in price. More and more consumer and commercial products, such as for example but not limited to, appliances, telecommunications devices, automobiles, security systems, full-house instant hot water heaters, thermostats, and the like are being controlled by these integrated circuit microcontrollers. Analog inputs for receiving sensor information and analog outputs for controlling functions are necessary for the application of these microcontrollers. Heretofore separate and discrete analog interfaces were used to connect the digital microcontroller to the outside world.
Analog input devices such as an analog-to-digital converter (ADC) in conjunction with a separate operational amplifier were used to convert a time-varying analog signal into digital representations thereof for application to digital inputs and use thereof by the microcontroller. Voltage and current levels were also detected by discrete integrated circuit voltage comparators that changed a digital output state when a certain analog value was present on the input of the comparator.
Different applications required different speeds for the ADC-Op Amp and the comparators. This was not a problem since the ADC-OP Amp and the comparators were separate integrated circuit devices that could be selected for the specific applications. Technology has now advanced to the point where the analog input and output devices can be fabricated on which the same integrated circuit die that the digital microcontroller and its support logic and memories are also fabricated.
A problem exists, however, in that these analog input microcontrollers must interface with very different analog input parameters such as speed, gain, offset, common mode rejection, linearity and the like. In addition, different applications of the analog input microcontroller may have restrictions on the amount of power available to run the microcontroller and its integral analog peripherals. Since there are so many different combinations of analog input and systems parameters, a great number of different types of integrated circuit analog input microcontrollers are required. This precludes any cost reductions because there is no economics of scale through the possibility of increased production quantities.
What is needed is an integrated circuit microcontroller having analog input peripherals that can be programmably adapted for measurement and control applications requiring different analog input parameters, and can be further mass-produced to reduce overall product costs.
The invention overcomes the above-identified problems as well as other shortcomings and deficiencies of existing technologies by providing on a single integrated die or multi-chip package (MCP) a microcontroller system having a configurable operational amplifier that can be programmed for specific characteristics and parameters which are adapted to various requirements in the measurement of analog signals for a specific application. In another embodiment of the invention, a plurality of configurable operational amplifiers, each being configurable with the same or a different characteristic than the others, is programmably selectable for a specific operation in combination with the microcontroller.
The configurable operational amplifier, according to the present invention, may comprise, for example, but not limited to, the following programmable features: programmable gain bandwidth product (GBWP), programmable selection of operational amplifier (op-amp) or comparator modes of operation, input offset zero calibration, ultra low input bias current, rail-to-rail input operation, and rail-to-rail output operation. The configurable op-amp may also be programmed to a xe2x80x9csleep modexe2x80x9d which further reduces system power requirements.
The programmable gain bandwidth product (GBWP) feature enables the configurable op-amp of the invention to be utilized for slow, medium or high speed applications. Conservation of power in battery powered applications is readily facilitated by configuring the op-amp in a low GBWP mode, since the op-amp will consume a minimum amount of power from the power supply (battery).
The programmable selection of operational amplifier (op-amp) or comparator modes of operation feature enables a configurable op-amp to also be utilized in an application as a comparator in combination with the microcontroller. This feature adds flexibility and increased capabilities in the application of the microcontroller system.
The input offset zero calibration feature may be used to minimize the input offset voltage of the op-amp. This feature enables the op-amp to be used for high gain applications, for example, but not limited to, instrumentation sensors such as temperature, pressure, vibration, humidity, gas, ozone, pH, vibration, battery charge and the like. The input offset zero calibration feature may be invoked on demand during start-up of the microcontroller system or at any time during operation thereof. This feature enables the op-amp to maintain an extremely low input offset voltage over the entire operating range of voltage and temperature which occurs during operation of the application.
The ultra low input bias current feature allows the op-amp to be used in very high impedance sensor applications.
The rail-to-rail input feature allows the op-amp to be used in applications requiring resolution of input signal values that are equal to or less than the power supply rails (such as voltages VDD or VSS).
The rail-to-rail output feature allows the op-amp to take advantage of the full input range of an analog-to-digital converter (ADC), i.e., maximum use of the total bit range (scale) of the ADC.
An advantage of the invention is the ability to minimize design time and inventory because multiple types of operational amplifiers do not have to be specified, purchased and/or kept in inventory.
Another advantage is simplification of manufacturing requirements by reducing the number of different types of microcontroller op-amp type integrated circuit parts needed and increasing the quality of the same type of part manufactured.
Still another advantage is producing a microcontroller system having analog input capabilities that may be used for a very broad range of applications, which further enhances the demand for a general purpose microcontroller system available on an integrated circuit die or in a MCP.
In an embodiment of the configurable op-amp, nulling of input offset voltage of the differential amplifier may be performed. In addition to the high speed or low power modes, the configurable op-amp may have a power down feature for further reducing power consumption of the integrated circuit. Furthermore the configurable op-amp may have a xe2x80x9cbolt-on compression preampxe2x80x9d which enables a common mode input voltage range from ground (VSS) to the power supply voltage (VDD), rail-to-rail input. This enables small or large signal operation of the configurable op-amp at or near either or both power supply voltages.
This bolt-on compression preamp performs a one to one voltage mapping of a rail to rail voltage input to an output which is not rail to rail. In an ac signal sense the circuit has less than unity gain. This allows the input differential stage of the operational amplifier to be in the saturation region of operation regardless of common mode voltage input. The only thing that is sacrificed is open loop gain which may be reduced by approximately 6 dB.
The configurable operational amplifier has a biasing circuit that allows for approximately a 10 to 1 power current consumption selection with resulting gain bandwidth product performance changes. The configurable operational amplifier also has a input voltage offset nulling circuit which is controlled by a small resistor and a current that is between the two emitters of the input differential transistor pair. The configurable operational amplifier may be designed around a folded cascode architecture so the entire circuit may scale with the biasing circuit.
Other and further features and advantages will be apparent from the following description of presently preferred embodiments of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings.